Many plants produce chemical defenses to protect themselves against being eaten. Still little is known about what makes these substances toxic to their consumers. Researchers at the Max Planck Institute for Chemical Ecology and the University of Münster have now investigated how plants produce toxins and store them in their tissues without harming themselves. In particular, they wanted to know whether the mechanisms of autotoxicity and its prevention share similar mechanisms as the toxic characteristics that provide defense against herbivores.

Autotoxicity and defense

For their experiments, they chose diterpene glycosides from Nicotiana attenuata plants, a wild tobacco species. “These substances occur at very high concentrations in the leaves of tobacco plants. But we had no idea why they were such effective defenses or why they could be so toxic to produce. So the situation was completely different from the other very abundant toxin that this plant produces, namely, nicotine. Nicotine is a specific neurotoxin. Since plants lack nerves and muscles, they offer no target for the toxin. So producing and storing nicotine does not harm plants,” says Ian Baldwin from the Department of Molecular Ecology at the Jena Max Planck Institute, where the study was carried out.

To their surprise, the researchers found that tobacco plants which had been transformed so they could no longer produced two proteins involved in the biosynthesis of the diterpene glycosides and thus also not form the defensive substances otherwise stored in the leaves in large amounts, showed conspicuous symptoms of self-poisoning: they were sick, unable to grow normally, and could no longer reproduce. Further experiments revealed that certain components of the cell membrane, so-called sphingolipids, had been attacked.

Targeting the cell membrane

Sphingolipids are substances found in all animals and plants, including the enemies of wild tobacco, the larvae of the tobacco hawkmoth Manduca sexta. The researchers therefore asked whether the sphingolipid metabolism could be the target of the diterpene glycosides. In fact, Manduca sexta caterpillars, which had fed on plants without diterpene glycosides, grew significantly better than larvae, which had fed on controls that contained the defensive chemicals. Analyses of the frass of Manduca sexta larvae, which had ingested diterpene glycosides with their food, provided further insights, as the degradation of the plant toxins during larval digestion is more or less in reverse order to the synthesis of the substances in the plant. Plants prevent self-harm by storing the defensive substances in a non-toxic form. However, when insects feed on the plant, a part of the non-toxic molecule is cleaved off and the chemical becomes activated or “armed.” “Interestingly, in both cases, in plants with incomplete diterpene glycoside biosynthesis and in feeding caterpillars, the target of the toxins is the sphingolipid metabolism,” says first author Jiancai Li.

Sphingolipids are mediators in many physiological processes. This makes the effect of diterpene glycosides on sphingolipid metabolism so intriguing. “Diterpene glycosides and their derivatives can have broad defensive functions against many agricultural pests and pathogenic fungi. At the same time, many human diseases, such as diabetes, cancers and some neurodegenerative diseases are also associated with elevated sphingolipid metabolisms,” says Shuqing Xu from the Institute for Evolution and Biodiversity at the University of Münster, who is one of the senior authors of the study. Physicians have been searching for effective substances to treat these diseases by inhibiting the sphingolipid metabolism. The diterpene glycosides studied here could be potential candidates for further investigations.

“Frassomics” — a new powerful tool to study interactions between organisms

The analysis of larval frass proved to be the key to success in this study. The scientists call this new approach “frassomics”: a combination of frass (larval droppings) and metabolomics — the analysis of all metabolites in an organism. “From this work, we realized that frassomics can be a very powerful research tool. The analysis of larval frass can provide metabolic clues about how what one organism produces is metabolized by consumer organisms,” says Ian Baldwin.

The scientists plan to gain more insights into the “digestive duets” that occur between plants and insects, in order to better understand ecological interactions between plants, insects and microorganisms.

“The opioid crisis and resulting overdose deaths in the United States are now well known, but what is less recognized is that there is a growing crisis of overdose deaths involving methamphetamine and other stimulants. However, unlike for opioids, there are currently no approved medications for treating methamphetamine use disorder,” said NIDA Director Nora D. Volkow, M.D. “This advance demonstrates that medical treatment for methamphetamine use disorder can help improve patient outcomes.”

The study known as the Accelerated Development of Additive Pharmacotherapy Treatment for Methamphetamine Use Disorder study, or ADAPT-2, was conducted from 2017 to 2019 at clinics in multiple community treatment programs nationwide and enrolled 403 adult volunteers ages 18 to 65 years with moderate to severe methamphetamine use disorder. All participants wished to reduce or cease use of the drug and were randomly assigned to the treatment or control group.

In each of two six-week stages, volunteers in the treatment group were given an injection of extended-release naltrexone, a drug used to treat opioid and alcohol use disorders, every three weeks and took daily extended-release tablets of bupropion, an antidepressant also used as a treatment to aid nicotine cessation. Those in the control group were given matched injectable and oral placebos over the same time periods. Investigators performed four urine drug screens at the end of each stage of the trial. Participants were considered to have responded to treatment if at least three of four urine screens were negative.

Overall, participants responded at a significantly higher rate in the treatment group. When screened during weeks five and six, 16.5% of those given the altrexone/bupropion combination responded, compared to only 3.4% of those in the control group. Similarly, when screened in weeks 11 and 12, 11.4% of the treatment group responded, compared to 1.8% of the control group. Researchers calculated that the number needed to treat (NNT) was 9. NNT is a way to describe the utility of a medical intervention that indicates the number of people who would need to receive a treatment for it to benefit one person. The investigators reported that, with an NNT of 9, naltrexone/bupropion’s benefit as a treatment for methamphetamine use disorder is similar to most medical treatments for mental health disorders, including antidepressants prescribed for depression or naltrexone prescribed for alcohol use disorder.

Participants in the treatment group were assessed to have fewer cravings than those in the placebo group and reported greater improvements in their lives as measured by a questionnaire called the Treatment Effectiveness Assessment. Importantly, there were no significant adverse effects associated with the dual medication treatment. Adherence to treatment was encouraged by adherence counseling and mobile app reminders and remained high at 77.4% and 82.0% in the treatment and placebo groups, respectively, in the final six weeks of the study.

“Long-term methamphetamine misuse has been shown to cause diffuse changes to the brain, which can contribute to severe health consequences beyond addiction itself,” said Madhukar H. Trivedi, M.D., of the University of Texas Southwestern Medical Center, Dallas, who led the trial. “The good news is that some of the structural and neurochemical brain changes are reversed in people who recover, underscoring the importance of identifying new and more effective treatment strategies.”

Methamphetamine use disorder is a serious illness often associated with severe medical and mental health complications and a risk of fatal overdose. Methamphetamine is a potent stimulant, and, like other addictive drugs, it hijacks the reward pathways in the brain by raising levels of dopamine, a brain chemical associated with repeating actions that cause pleasurable feelings.

Finding treatments that disrupt these processes has been challenging for scientists. Research suggests bupropion may alleviate dysphoria associated with methamphetamine withdrawal by acting on the dopamine and norepinephrine systems. Alleviating dysphoria may in turn reduce cravings and help prevent return to methamphetamine use. Naltrexone may reduce the euphoric effects and cravings associated with taking methamphetamine. In previous clinical studies, however, both bupropion and naltrexone administered alone showed limited, inconsistent efficacy in treating methamphetamine use disorder. Now, in combination, these compounds seem to have an additive or synergistic effect.

While there are U.S. Food and Drug Administration-approved medications for other substance use disorders, no medications have yet received FDA approval for methamphetamine use disorder. The effectiveness of this medication combination is progress toward improving treatment of this addiction.

The investigators recommend that future research build on this work by testing if longer naltrexone/bupropion treatment or concurrent behavioral therapy, such as contingency management, brings still better responses. Contingency management , which uses motivational incentives and tangible rewards to help a person attain their treatment goals, has demonstrated to be the most effective therapy for stimulant use disorders but is not widely used, stemming in part from a policy limiting the monetary value of incentives allowable as part of treatment.

Researcher Paul Patterson, professor of poultry science, College of Agricultural Sciences, suggests the technology has merit for commercial application in the egg industry.

“This study is unique because it scaled-up and applied components of standard egg processing to a conveyor and sanitizing eggs in a commercial setting,” he said. “In the absence of water or other chemical sanitizers, this technology has the potential to achieve significant — equal or greater — microbial reductions than some currently available technologies.”

Every year in the United States, an average of 287 eggs are consumed per person, and more than 14.1 billion eggs are set in hatchery incubators to produce chicks destined for the egg and meat bird industries. By reducing the microbial load on eggs, foodborne illness outbreaks associated with eggs and poultry meat can be reduced while chick health is maintained.

The egg industry currently uses sanitizers and detergents to decontaminate eggs and wash off any physical debris, while low-intensity ultraviolet light has been used as an additional antimicrobial step. However, pulsed ultraviolet light is more effective, explained lead researcher Josh Casser, doctoral candidate in animal science, because it delivers a higher intensity of ultraviolet light to the surface of the eggshell. That results in a greater microbial reduction in a shorter period of time than conventional ultraviolet light treatment.

In this study, the surfaces of shell eggs were inoculated with nonpathogenic bacteria strains used for research and were treated with pulsed ultraviolet light derived from a xenon flashlamp. Eggs were exposed on a modified egg-carrying conveyor that provided complete rotation of eggs under the flashlamp.

The novel conveyor devised for the experiment was instrumental in achieving acceptable decontamination, Casser noted, adding that the xenon flashlamps could be scaled up and customized for any commercial installation.

“As the egg rotates on its long axis along the way, the entire surface of the eggshell is exposed to the pulsed ultraviolet light energy, and the 27 seconds of exposure in our experiment resulted in an acceptable germicidal response,” he said. “At three pulses per second, each egg is exposed to nearly 90 pulses, and each pulse has a duration of 360 microseconds — an extremely short duration pulse.”

The researchers, who recently published their results in Poultry Science, found that pulsed ultraviolet light treatment inactivated two different microbial strains, with greater energy resulting in a greater germicidal response.

The study also evaluated the effects of pulsed ultraviolet light treatment of hatching eggs on both embryo and chick growth. Using the same system, four batches of 125 fertile eggs were treated with the same and greater intensities of pulsed ultraviolet light. After processing, eggs were placed in a commercial incubator under normal incubation conditions.

There was no significant effect of the pulsed ultraviolet light treatment on percent fertility, hatchability or hatch. Also, there were no significant effects on post-hatch observations, including chick livability and average bird weight at hatch or at 42 days of age.

“Our research supports the application of pulsed ultraviolet light as an effective antimicrobial intervention for both table and hatching eggs,” Cassar said. “If the egg industry embraces pulsed ultraviolet light technology and applies it in its processing operations, food safety would be improved because of the reduced pathogen presence on the surface of the eggs. And that matters because 9% of all foodborne illness in the U.S. is associated with eggs.”

The technology is especially promising because it appears to have no negative consequences for the vital hatching-eggs component of the business, even at 10 times the UV-light intensity used in the table egg study, Patterson pointed out. Hatcheries produce the replacement stock for both the egg and broiler flocks of the poultry industry, including turkeys.

“Our research showed that there are no negative effects on hatching eggs and the embryos and chicks that are derived from those treated eggs,” he said. “Using pulsed ultraviolet light before incubation in a hatchery setting would improve chick health, would avoid some of the financial constraints caused by poor chick quality resulting from chicks getting sick from early exposure to microbial pathogens, and potentially would improve the food safety of poultry meat.”

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Materials provided by Penn State. Original written by Jeff Mulhollem. Note: Content may be edited for style and length.

“While we knew that the memories of people with primary progressive aphasia were not affected at first, we did not know if they maintained their memory functioning over years,” said study author M. Marsel Mesulam, M.D., of Northwestern University Feinberg School of Medicine in Chicago and a Fellow of the American Academy of Neurology. “This has been difficult to determine because most memory tests rely on verbal skills that these people have lost or are losing.”

The study included 17 people with primary progressive aphasia associated with Alzheimer’s disease. They were compared to 14 people who had typical Alzheimer’s disease with memory loss.

Researchers tested memory skills of the people with primary progressive aphasia by showing them pictures of common objects. After waiting 10 minutes, they were shown the same pictures along with others and had to indicate whether they had seen the picture before. This test was given once and then again an average of 2.4 years later. The people with typical Alzheimer’s disease listened to a list of common words and were later given the same words along with others and asked to choose the ones they had heard before. They were tested once and then again an average of 1.7 years later.

Both groups also had tests of their language skills. Brain scans were taken of the people with primary progressive aphasia to look at how the disease was affecting their brains, especially in the areas related to memory.

The people with primary progressive aphasia had no decline in their memory skills when they took the tests a second time. At that point, they had been showing symptoms of the disorder for an average of six years. In contrast, their language skills declined significantly during the same period. For the people with typical Alzheimer’s disease, their verbal memory and language skills declined with equal severity during the study.

Researchers had brain autopsies from eight of the people with primary progressive aphasia and all of the people with typical Alzheimer’s disease. The people with primary progressive aphasia had similar amounts of the plaques and tangles that are signs of Alzheimer’s disease as the people with typical Alzheimer’s, Mesulam said. Left sided asymmetry of brain shrinkage and a lower incidence of brain proteins known as ApoE4 and TDP-43 were identified as potential contributors to the preservation of memory in this rare type of Alzheimer’s disease.

“More research is needed to help us determine what factors allow these people to show this resilience of memory skills even in the face of considerable Alzheimer’s disease pathology in the brain,” Mesulam said.

Limitations of the study are the relatively small sample size and that autopsies were not available for all of the primary progressive aphasia cases.

The study was supported by the National Institute on Deafness and Other Communication Disorders, National Institute of Neurological Disorders and Stroke, The Davee Foundation and The Jeanine Jones Fund.

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Materials provided by American Academy of Neurology. Note: Content may be edited for style and length.